PROJECT SUMMARY/ABSTRACT Exosomes are nanoparticles that play an essential role in cell-to-cell communication by shuttling a variety of cargos among tissues. Exosome cargos regulate more than 60% of human genes and have been implicated in virtually all physiological and pathological conditions. Supported by compelling preliminary data, this proposal will test the central hypothesis that developing an exosome and cargo tracking (ECT) mouse will provide a tool for identifying the donor and recipient tissues of exosome subsets and assessing the cargos in these exosomes. This project?s long-term goal is to enable the widespread use of this ECT mouse model, which will accelerate the rate of discovery in biomedical and exosome biology research across a variety of fields and illnesses. The main objective of this project will be to develop a tamoxifen-inducible ECT mouse model that allows investigators to exercise spatial and temporal control over the expression of endogenous exosomes in which the exosome marker CD63 is fused to near-infrared protein (iRFP); this will be achieved through one specific aim: to develop and optimize an ECT mouse to assess the origin, destination, and cargo of endogenous exosomes. The ECT vector was designed to allow for sorting of tissue-specific, iRFP-labeled exosomes by streptavidin- coated magnetic beads for subsequent cargo analysis. ECT vector design and iRFP-based exosome capture are methodologically innovative. The proposed work is conceptually innovative because the ECT mouse will be the first model to exercise spatial and temporal control over exosome biogenesis and assess exosome biogenesis, trafficking, and cargo content. One of the strengths of this proposal is that the ECT mouse has already been developed and funding is sought for optimizing the mouse. This project does not overlap with active grants in the NIH RePORTER database (i.e., the project will be unique in the NIH grants portfolio). This project is of great significance and impact because it will break new ground for developing strategies that use exosomes and their cargos in the diagnosis, prevention, and treatment of major diseases such as cancer, cognitive decline in the elderly, and obesity-induced non-alcoholic fatty liver disease. Scholars supported by various NIH institutes will benefit from access to the ECT mouse, and there are many applications in areas relevant to the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging, the National Institute of Neurological Disorders and Stroke, the National Cancer Institute, and the National Institute of Allergy and Infectious Diseases. Therefore, this application delivers on the priorities identified in PAR-16-141, which seeks proposals to develop animal models that are applicable to the research interests of two or more categorical NIH institutes.